In order to reduce the weight of the driven rotating body while ensuring the strength thereof, Patent Document 1 discloses a valve opening/closing timing control device that includes a driven rotating body that is configured with: a cylindrical outer circumferential member that is made of a lightweight aluminum-based material, and that constitutes a part on the outer circumference side; and a cylindrical inner circumferential member that is made of an iron-based material having a higher strength than the aluminum-based material, and that constitutes a part on the inner circumference side, the outer circumferential member and the inner circumferential member being coaxially integrated into one piece.
In the driven rotating body included in this valve opening/closing timing control device: the outer circumferential member has a partitioning portion that is integrated therewith and that partitions a fluid pressure chamber into an advancing chamber and a retarding chamber; the inner circumferential member has a protruding portion that is integrated therewith and that protrudes outward in the radial direction; and the protruding portion is embedded in the outer circumferential member inside the partitioning portion, so that the outer circumferential member and the inner circumferential member are prevented from rotating relative to each other.
An advancing channel for supplying a pressurized fluid, which is in communication with the advancing chamber, and a retarding channel for supplying a pressurized fluid, which is in communication with the retarding chamber, are formed to penetrate through the driven rotating body in the radial direction thereof.